Measurements of density as a function of temperature will be made on lipid bilayers using an accurate differential dilatometer developed under the preceding grant. This instrument permits equilibrium measurements to be made and the temperature control is better than 0.01 degrees C, which are important for phase transition studies. The density measurements together with calorimetric measurements and elementary theory will be used to provide quantitative estimates of intermolecular interaction changes. Particular lipids to be investigated include single component samples of phosphotidic acids, phosphatidylserines, phosphatidylglycerols and sphingomyelins, as well as purer samples of lecithins and phosphatidylethanolamines. The phase diagrams and volume changes of mixtures of lipids, of lipids and cholesterol, and lipids and proteins will be investigated and compared to transitions observed in cell membranes.